Sterilization of objects such as medical devices or surgically implantable devices or prostheses has traditionally been done by a variety of methods including steam or dry heating, ultraviolet, x-ray, or gamma-ray irradiation, plasma sterilization, conventional ion beam irradiatiation, and exposure to sterilant gases or germicidal fluids.
Gas-cluster ions are formed from large numbers of weakly bound atoms or molecules sharing common electrical charges and they can be accelerated to have high total energies. Gas-cluster ions disintegrate upon impact and the total energy of the cluster ion is shared among the constituent atoms. Because of this energy sharing, the atoms are individually much less energetic than in the case of un-clustered conventional ions and, as a result, the atoms only penetrate to much shallower depths than would conventional ions. Surface effects can be orders of magnitude stronger than corresponding effects produced by conventional ions, thereby making important micro-scale surface modification effects possible that are not possible in any other way.
The concept of gas-cluster ion-beam (GCIB) processing has only emerged in recent decades. Using a GCIB for dry etching, cleaning, and smoothing of materials, as well as for film formation is known in the art and has been described, for example, by Deguchi, et al. in U.S. Pat. No. 5,814,194, “Substrate Surface Treatment Method”, 1998. Because ionized gas-clusters containing on the order of thousands of gas atoms or molecules may be formed and accelerated to modest energies on the order of a few thousands of electron volts, individual atoms or molecules in the clusters may each only have an average energy on the order of a few electron volts. It is known from the teachings of Yamada in, for example, U.S. Pat. No. 5,459,326, that such individual atoms are not energetic enough to significantly penetrate a surface to cause the residual sub-surface damage typically associated with plasma polishing or conventional monomer ion beam processing. Nevertheless, the clusters themselves are sufficiently energetic (some thousands of electron volts) to effectively etch, smooth, or clean hard surfaces, or to perform other shallow surface modifications.
Because the energies of individual atoms within a gas-cluster ion are very small, typically a few eV, the atoms penetrate through only a few atomic layers, at most, of a target surface during impact. This shallow penetration of the impacting atoms means all of the energy carried by an entire cluster ion is consequently dissipated in an extremely small volume in the top surface layer during an extremely short time interval. This is different from the case of ion implantation, which is normally done with conventional ions and where the intent is to penetrate into the material, sometimes penetrating several thousand angstroms, to produce changes in both the surface and sub-surface properties of the material. Because of the high total energy of the cluster ion and extremely small interaction volume of each cluster, the deposited energy density at the impact site is far greater than in the case of bombardment by conventional ions and the extreme conditions permit material modifications not otherwise achievable.
Irradiation by GCIB has been successfully applied in a variety of surface modification processes including cleaning, smoothing, surface infusion, deposition, etching, and changing surface characteristics such as making a surface more or less wettable. The cleaning, smoothing, etching, and wettability modification processes (for example) are sometimes useful for improving the surfaces of medical devices, surgical implants, and medical prostheses. It is desirable and necessary that many types of medical devices, implants, and prostheses be sterile for use in their intended applications.
It is therefore an object of this invention to provide methods and apparatus for surface sterilization of objects including medical devices, surgical implants, and/or medical prostheses by GCIB irradiation.
It is another object of this invention to provide methods and apparatus for multi-step processing of objects including a step of surface sterilization by GCIB irradiation in combination with another GCIB surface processing step on the same object.
It is a further object of this invention to provide methods and apparatus for surface sterilization of objects, without significantly elevating the temperature of the bulk of the object and without the use of toxic materials.